In collaboration with a University of Minnesota sustainable forestry researcher, Urban Growler is using an altogether unusual ingredient in a limited-edition beer.

The ramón nut, which grows in the Guatemalan rain forest, imparts a coffee-chocolate flavor upon roasting — the perfect match for a batch of stout now available at the St. Paul microbrewery. (2325 Endicott St., St. Paul, 651-340-5793, urbangrowlerbrewing.com)

The Guatemalan ramón nut.

David Wilsey, a researcher at the Humphrey School of Public Affairs, was investigating how the ancient Mayan food source can be a tool of economic empowerment for people living where it grows, when he got the idea to brew the nut into beer. Working with a group of his students, Wilsey secured a grant and approached Urban Growler’s owners. Their first batch last spring sold out rapidly. It’s back on tap till it runs out.